1. Field of the Invention
The present invention relates to a vacuum apparatus, and especially the present invention relates to a vacuum apparatus using an ion gun.
2. Description of the Prior Art
In a film deposition process using an ion gun, there are some representative film deposition methods such as an ion beam sputtering method in which ion beam generated by an ion source (plasma) collides against a target and sputtered particles from a target surface form a film, and an ion assist evaporation method in which thin film material is vaporized by an electron gun and the ion gun assists to form a film, or the like. The ion gun is also used in an ion beam etching method, in which etching is carried out with the use of an ion beam, in addition to the film deposition process.
In these processes, there are, for example, three types of ion guns that are used, which are classified according to a method for generating plasma therein. The representative types of ion guns are an RF ion gun type in which RF (radio frequency) power is applied to generate plasma, a filament type in which plasma is generated by a hot filament, and a hollow cathode type in which DC power is applied to a hollow cathode.
Of these types of ion guns, the RF ion gun type has a significant advantage in that the ion gun uses oxygen gas and can process insulating material for a long time so that the RF ion gun becomes indispensable to a film deposition apparatus and an evaporation apparatus for manufacturing an optical filter or the like, especially for the telecommunication market. A narrow-band filter for communication use, for example, is composed of laminated 100 layers or more SiO2 and Ta2O3 films so that it takes several tens of hours to form the films. The RF ion gun used in this case needs to have a performance to stably discharge for a long time, as one of the essential requirements.
In the case of ion beam sputtering, a summary of an apparatus using the RF ion gun will be hereinafter described.
In FIG. 5, the reference numeral 101 indicates one example of conventional film deposition apparatuses using the RF ion gun. The film deposition apparatus 101 has a vacuum chamber 111.
An RF ion gun 112 and an electron generator (a neutralizer) 113 are provided on the wall of the vacuum chamber 111. The RF ion gun 112 is connected to a power source 119 via a matching box 102.
A target 115 is disposed in the vacuum chamber 111. Starting the power source 119 after air is evacuated from the vacuum chamber 111, power for generating ions is supplied to the RF ion gun 112 via the matching box 102 so that the ions are generated inside the RF ion gun 112.
Consequently, the electron generator 113 is started. When an ion beam 121 is emitted from the RF ion gun 112 with discharging electrons 122 from the electron generator 113, the electrons neutralize positive ions in the ion beam 121. Since neutral particles are applied to the target 115, atoms of the target 115 are sputtered as sputtered particles 123.
A substrate 117, as an object on which a film is to be deposited, is disposed in parallel with the target 115. When the sputtered particles 123 adhere to the substrate 117, a thin film is formed on the surface of the substrate 117.
The impedance inside the foregoing RF ion gun 112 greatly varies between when the ions are generated, and when the ions are stably emitted.
Thus, the matching box 102 of a prior art has variable capacitors 134 and 135 as shown in FIG. 6. An input terminal 131 on the side of the power source 119 is grounded via the variable capacitor 135, and is connected to an output terminal 132 on the side of the RF ion gun 112 via a series connected circuit of the other variable capacitor 134 and a coil 133.
In the matching box 102 having the above-discussed structural arrangement, it is possible to vary the impedance of the matching box 102 by varying the capacitance of the variable capacitors 134 and 135.
However, in order to vary the capacitance in the variable capacitors 134 and 135, the electrode composing the capacitor is moved to vary the distance between electrodes. Accordingly, there is the disadvantage that it takes several hundreds milliseconds to several seconds to match the impedance of the matching box 102 to that inside the RF ion gun 112.
Impedance matching speed has not so far been given importance in the film deposition apparatus 101 having the RF ion gun 112. However, recently, in a case of a film deposition process of a narrow-band filter for communication use, for example, continuous film deposition of several tens of hours is necessary; and the film thickness accuracy of ±0.001% is required to laminate 100 or more thin films.
In this case, if generation of plasma is stopped due to the occurrence of arc discharge or the like caused by contamination of the electrode or the like, the matching box 102 with the mechanical variable capacitances takes several seconds or more only to match impedance at restart. Accordingly, even if the RF ion gun 112 is restarted, the produced filter becomes defective because the film deposition is stopped for several seconds or more.
In other words, a significant problem occurs when an accurate film forming process of several tens of hours ends in failure because of only one time of discharge interruption of several seconds. The references relating to the conventional art are follows: JP09-161704A, JP09-92199A and JP2000-165175A.